The present invention relates to read channels in data storage devices, and in particular, to controlling a read channel dynamically based on both decision-aided error and envelope-derived error.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In optical data storage read channels, an electrical signal, often called RF or HF, is generated by a photo detector. A gain loop is used to amplify the RF signal to full dynamic range of the analog to digital converter (ADC). An offset loop is used to compensate for low frequency DC drifts. The error signal driving these two loops can be envelope-derived error (EE) and decision-aided error (DE).
Regarding EE, an envelope detector may be used to detect top and bottom envelopes of the ADC output. The gain error can be measured as the distance between the top and bottom envelopes in reference to the desired amplitude; the offset error can be measured as mean of the top and bottom envelope in reference to zero.
Regarding DE, a decision can be made by a slicer that follows a limit equalizer. An example can be seen in the white paper “Blu-ray Disc: Physical Format Specifications for BD-ROM” dated January 2005. Assuming that decisions are sufficiently accurate, the decision convolved with the target should match the equalizer output, therefore their difference reflects gain and offset errors.
(Further regarding decision-aided error, decisions can be generated data detectors other than a slicer after a limit equalizer: e.g., a slicer without a limit equalizer, fixed-delay tree search detector, or a Viterbi detector after a finite impulse response (FIR) filter, etc. For an example of the fixed-delay tree search detector, see J. Moon and R. L. Carley, “Performance comparison of detection methods in magnetic recording”, IEEE Transactions on Magnetics, Volume 26, Issue 6, pp. 3155-3172 (1990).)
In a conventional channel, the decision to use EE or DE is a fixed selection specified by register settings.